Color separation element array, image sensor including the color separation element array, and image pickup apparatus including the color separation element array

ABSTRACT

A color separation element array includes color separation elements which are two-dimensionally arranged to separate an incident light according to a wavelength such that a light of a first wavelength is directed to a first direction and a light of a second wavelength that is different from the first wavelength is directed to a second direction that is different from the first direction. Each of the color separation elements includes a first element and a second element that are sequentially arranged along a traveling direction of the incident light, and the first element and the second element of the color separation elements are symmetrically shifted with respect to a center area of the color separation element array, to be aligned to fit to the traveling direction of the incident light that is obliquely incident.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.14/738,396 filed Jun. 12, 2015, which claims priority from Korean PatentApplication No. 10-2014-0072294, filed on Jun. 13, 2014, in the KoreanIntellectual Property Office. The disclosures of the above-listedapplications are incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The present disclosure relates to a color separation element array, animage sensor including the color separation element array, and an imagepickup apparatus including the color separation element array, and moreparticularly, to a color separation element array that may improve acolor separation efficiency at an edge portion thereof where light isobliquely incident, and to an image sensor and an image pickup apparatususing the color separation element array.

2. Description of the Related Art

Color display devices or color image sensors display an image of variouscolors or detect a color of incident light by using a color filter. AnRGB color filter method, in which, for example, a green filter isarranged at two pixels of four pixels and a blue filter and a red filterare arranged in the other two pixels, is most widely employed by acurrently used color display device or color image sensor. In additionto the RGB color filter method, a CYGM color filter method may beemployed in which color filters of cyan, yellow, green, and magenta,which are complementary colors, are respectively arranged at fourpixels.

However, a color filter may have a low light use efficiency because thecolor filter absorbs light of other colors except for filtered light.For example, when an RGB color filter is in use, only ⅓ of the incidentlight is transmitted and the other portion, that is, ⅔, of the incidentlight is absorbed. Accordingly, the light use efficiency may be about33%. Accordingly, for the color display device or a color image sensor,most of a light loss is generated in the color filter.

Recently, to improve the light use efficiency of the color displaydevice or color image sensor, a color separation element is being usedinstead of the color filter. The color separation element may separatecolors of the incident light by using the diffraction or refractioncharacteristics of a light that varies according to a wavelength of thelight. The colors separated by the color separation element may betransferred to pixels corresponding to the transferred colors.Accordingly, use of the color separation element may achieve a higherlight use efficiency as compared to a case of using the color filter.

SUMMARY

One or more exemplary embodiments include a color separation elementarray, an image sensor including the color separation element array, andan image pickup apparatus including the color separation element array.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented exemplary embodiments.

According to an aspect of an exemplary embodiment, a color separationelement array includes a plurality of color separation elements arrangedin two dimensions and separating an incident light according to awavelength such that, of the incident light, a light of a firstwavelength is directed to a first direction and a light of a secondwavelength that is different from the first wavelength is directed to asecond direction that is different from the first direction, in whicheach of the plurality of color separation elements includes a firstelement and a second element that are sequentially arranged according toa traveling direction of the incident light, and the first element andthe second element of at least one of the plurality of color separationelements are shifted with respect to each other.

The first and second elements of at least two of the color separationelements may be shifted with respect to each other differently.

The first element and the second element of one of the plurality of thecolor separation elements arranged in a center area of the colorseparation element array may be arranged such that center portions ofthe first element and the second element are aligned with each other,and the first element and the second element of each of the plurality ofthe color separation elements arranged in an area other than the centerarea of the color separation element array may be arranged to be shiftedfrom each other.

The first element may be further shifted toward the center area of thecolor separation element array than the second element

A shift distance between the first element and the second element mayincrease as a distance from the center area of the color separationelement array increases.

The first element and the second element may be symmetrically shiftedwith respect to the center area of the color separation element array,and the first element and the second element of the plurality of thecolor separation elements may be shifted to be aligned to fit to atraveling direction of light that is obliquely incident.

The color separation element array may further include a transparentdielectric layer, in which the plurality of color separation elementsare buried in the transparent dielectric layer, and a refractive indexof the first element and a refractive index of the second element aregreater than that of the transparent dielectric layer.

The refractive index of the first element and refractive index of thesecond element may be identical to each other.

The refractive index of the first element and refractive index of thesecond element may be different from each other.

Each of the plurality of color separation element may further include athird element that is arranged following the second element along thetraveling direction of the incident light.

A width of the second element may be smaller than a width of the firstelement, and a width of the third element may be smaller than the widthof the second element.

According to another aspect of an exemplary embodiment, an image sensorincludes a pixel array including a plurality of pixels arranged in twodimensions and detecting light, and a color separation element arrayincluding a plurality of color separation elements arranged in twodimensions and separating an incident light according to a wavelengthsuch that light of different wavelengths are incident on differentpixels, in which each of the plurality of color separation elementsincludes a first element and a second element that are sequentiallyarranged according to a traveling direction of the incident light, andthe first element and the second element of at least one of theplurality of color separation elements are shifted with respect to eachother.

The first element and the second element of one of the plurality of thecolor separation elements arranged in a center area of the colorseparation element array may be arranged such that center portions ofthe first element and the second element are aligned with each other,and the first element and the second element of each of the plurality ofthe color separation elements arranged in an area other than the centerarea of the color separation element array may be arranged to be shiftedfrom each other.

The first element may be further shifted toward the center area of thecolor separation element array than the second element

A shift distance between the first element and the second element mayincrease as a distance from the center area of the color separationelement array increases.

The first element and the second element may be symmetrically shiftedwith respect to the center area of the color separation element array,and the first element and the second element of the plurality of thecolor separation elements may be shifted to be aligned to fit to atraveling direction of light that is obliquely incident.

According to another aspect of an exemplary embodiment, an image pickupapparatus includes an objective lens, and an image sensor converting alight focused by the objective lens to an electric image signal, inwhich the image sensor includes a pixel array including a plurality ofpixels arranged in two dimensions and detecting light, and a colorseparation element array including a plurality of color separationelements arranged in two dimensions and separating an incident lightaccording to a wavelength such that light of different wavelengths areincident on different pixels, each of the plurality of color separationelements includes a first element and a second element that aresequentially arranged according to a traveling direction of the incidentlight, and the first element and the second element of at least one ofthe plurality of color separation elements are shifted with respect toeach other.

The first element and the second element of one of the plurality of thecolor separation elements arranged in a center area of the colorseparation element array may be arranged such that center portions ofthe first element and the second element are aligned with each other,and the first element and the second element of each of the plurality ofthe color separation elements arranged in an area other than the centerarea of the color separation element array may be arranged to be shiftedfrom each other.

The first element may be further shifted toward the center area of thecolor separation element array than the second element, a shift distancebetween the first element and the second element increases as a distancefrom the center area of the color separation element array may increase,and the first element and the second element may be symmetricallyshifted with respect to the center area of the color separation elementarray.

The first element and the second element of the plurality of the colorseparation elements may be shifted to be aligned to fit to a travelingdirection of a chief light that passes through the objective lens.

The image sensor may further include a transparent dielectric layerarranged on a surface of the pixel array, and the plurality of colorseparation elements may be buried in the transparent dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become more apparent by describingcertain exemplary embodiments with reference to the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view schematically illustrating an imagepickup apparatus including a color separation element array and an imagesensor according to an exemplary embodiment;

FIG. 2 is a plan view exemplarily illustrating a positional relationshipbetween pixels of an image sensor and color separation elements;

FIG. 3 is a cross-sectional view exemplarily illustrating a pixelstructure of the image sensor of FIG. 2;

FIG. 4 is a cross-sectional view exemplarily illustrating another pixelstructure of the image sensor of FIG. 2;

FIG. 5A is a cross-sectional view exemplarily illustrating a positionalrelationship between a first element and a second element of a colorseparation element when a light is perpendicularly incident on an imagesensor;

FIGS. 5B and 5C are cross-sectional views exemplarily illustrating indetail a positional relationship between the first element and thesecond element of the color separation element when a light is obliquelyincident on the image sensor;

FIGS. 6A and 6B are cross-sectional views illustrating a change in thepositions of the first element and the second element of the colorseparation element according to a change in a light incident angle;

FIGS. 7A, 7B, 8A, 8B, 9A, and 9B are cross-sectional views exemplarilyillustrating color separation elements according to various exemplaryembodiments;

FIG. 10 is a plan view exemplarily illustrating shift forms of firstelements and second elements according to the positions of a pluralityof color separation elements in the image sensor; and

FIG. 11 is a graph exemplarily showing color separation efficiencyaccording to a change in a light incident angle.

DETAILED DESCRIPTION

Certain exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, like drawing reference numerals are usedfor like elements, even in different drawings. The matters defined inthe description, such as detailed construction and elements, areprovided to assist in a comprehensive understanding of the exemplaryembodiments. However, it is apparent that the exemplary embodiments canbe practiced without those specifically defined matters. Also,well-known functions or constructions are not described in detail sincethey would obscure the description with unnecessary detail.

A color separation element array, an image sensor including the colorseparation element array, and an image pickup apparatus including thecolor separation element array are described in detail with reference tothe accompanying drawings. In the following descriptions, like referencenumerals refer to like elements. In the drawings, the size of eachelement is exaggerated for clarity and convenience of explanation. Also,in the following description of a layer structure, when a layer isdescribed to exist “on” or “above” another layer, the layer may existdirectly on or indirectly above the other layer, or a third layer may beinterposed therebetween.

FIG. 1 is a cross-sectional view schematically illustrating an imagepickup apparatus 200 and an image sensor 100 including a colorseparation element array according to an exemplary embodiment. Referringto FIG. 1, the image pickup apparatus 200 according to the presentexemplary embodiment may include an objective lens 210 and the imagesensor 100 for converting light focused by the objective lens 210 to anelectric image signal. The image sensor 100 may include a pixel array110 having a plurality of pixels detecting light and arranged in twodimensions (2D), and the color separation element array having aplurality of color separation elements 130 arranged in 2D. The imagesensor 100 may further include a transparent dielectric layer 120arranged on a surface of the pixel array 110. The color separationelements 130 may be buried in the transparent dielectric layer 120.

The color separation elements 130 are arranged at a light incident sideof the pixel array 110 and each separate the incident light according tothe wavelength of the incident light such that light of differentwavelengths may be incident on different pixels. The color separationelements 130 may separate colors by changing traveling paths of lightaccording to the wavelengths of the light by using the diffraction orrefraction characteristics of the light that vary according to thewavelengths. For example, the color separation elements 130 are formedin various shapes such as a rod shape having a transparent symmetric orasymmetric structure or a prism shape having an inclined surface, whichare well known, and a variety of designs may be available according to adesired spectrum distribution of an exit light. Light use efficiency maybe increased by using the color separation elements 130 to optimize aspectrum distribution of light incident on the respective pixels to fitto the pixels. A positional relationship between the pixels of the imagesensor 100 and the color separation elements 130 may be variouslydesigned according to the color separation characteristics of the colorseparation elements 130.

For example, FIG. 2 is a plan view exemplarily illustrating a positionalrelationship between the pixels of the image sensor 100 and the colorseparation elements 130. Referring to FIG. 2, the image sensor 100 mayinclude the pixel array 110 having a plurality of photodetector pixelsPx1, Px2, and Px3 arranged in the form of a 2D matrix having a pluralityof rows and columns. For example, as illustrated in FIG. 2, only thefirst pixels Px1 may be arranged in a first pixel row P1, and the secondpixels Px2 and the third pixels Px3 may be alternately arranged in asecond pixel row P2 that is adjacent to the first pixel row P1. Thefirst pixel row P1 and the second pixel row P2 may be alternatelyarranged in a vertical direction. The color separation elements 130 maybe arranged facing the second pixels Px2 in the second pixel row P2.

FIG. 3 is a cross-sectional view exemplarily illustrating a structure ofthe first pixel Px1 arranged in the first pixel row P1 of the imagesensor 100 of FIG. 2. Referring to FIG. 3, the first pixel Px1 mayinclude a light sensing layer 111, a color filter layer 112 arranged ona light incident surface of the light sensing layer 111, the transparentdielectric layer 120 arranged on the color filter layer 112, and a microlens 141 arranged on the transparent dielectric layer 120 to focus theincident light on the light sensing layer 111. The light sensing layer111 converts the incident light to an electric signal according to theintensity of the incident light. In such a structure, the incident lightmay be focused by the micro lens 141 on the light sensing layer 111 bypassing through the transparent dielectric layer 120 and the colorfilter layer 112. The color filter layer 112 may include a first colorfilter CF1 that transmits only a light in a first wavelength band of theincident light. Accordingly, the first pixel Px1 may detect only thelight in the first wavelength band.

FIG. 4 is a cross-sectional view exemplarily illustrating a structure ofthe second and third pixels Px2 and Px3 arranged in the second pixel rowP2 of the image sensor 100 of FIG. 2. Referring to FIG. 4, the secondpixel row P2 may include the light sensing layer 111, a color filterlayer 112 arranged on a light incident surface of the light sensinglayer 111, the transparent dielectric layer 120 arranged on the colorfilter layer 112, the color separation elements 130 arranged in thetransparent dielectric layer 120 of the second pixel Px2, and a microlens 142 arranged on the transparent dielectric layer 120 to focus theincident light on the color separation elements 130. The color filterlayer 112 may include a second color filter CF2 that is arranged in thesecond pixel Px2 to transmit only a light in a second wavelength bandand a third color filter CF3 arranged in the third pixel Px3 to transmitonly a light in a third wavelength band. The color separation elements130 may be buried in the transparent dielectric layer 120 and may befixed by being surrounded by the transparent dielectric layer 120.

In the above structure, while passing through the color separationelements 130, the light focused by the micro lens 142 may be separatedinto a light C2 of a second wavelength band and a light C3 of a thirdwavelength band by the color separation elements 130. The colorseparation elements 130 may be designed, for example, to change atraveling direction of the light C3 of the third wavelength band of theincident light into two inclined lateral directions without changing atraveling direction of the light C2 of the second wavelength band. Then,the light C2 of the second wavelength band may pass through the colorseparation elements 130 and may be incident on the light sensing layer111 of the second pixel Px2 disposed directly under the color separationelements 130. On the other hand, after passing through the colorseparation elements 130, the light C3 of the third wavelength band maybe incident on the light sensing layer 111 of each of the third pixelsPx3 disposed at the opposite sides of the second pixel Px2.

In the example illustrated in FIGS. 2 to 4, in the first color filterCF1 of the first pixel Px1, only about 33% of the incident light istransmitted and arrives at the light sensing layer 111 as in a pixelstructure of the related art. In contrast, in the second color filterCF2 of the second pixel Px2 and the third color filter CF3 of the thirdpixel Px3, since a ratio of a color corresponding to each of the colorfilters CF2 and CF3 is high, transmissivity of light increases comparedto the pixel structure of the related art. Accordingly, light useefficiency in the second pixel Px2 and the third pixel Px3 may beincreased. For example, the first wavelength band may be green, thesecond wavelength band may be blue, and the third wavelength band may bered. In other words, the first pixel Px1 may be a green pixel, thesecond pixel Px2 may be a blue pixel, and the third pixel Px3 may be ared pixel.

The structure of the pixel array 110 of the image sensor 100 and thecharacteristics of the color separation elements 130 illustrated inFIGS. 2 to 4 are a mere example to help understanding and are notlimited to the exemplary embodiment illustrated in FIGS. 2 to 4. Avariety of color separation characteristics may be selected according tothe design of the color separation elements 130. A variety of structuresof the pixel array 110 may be selected according to the color separationcharacteristics of the color separation elements 130. Also, a part orthe entire of the micro lenses 141 and 142 and the color filters CF1,CF2, and CF3 may be omitted according to the design.

Referring back to FIG. 1, the objective lens 210 focuses an image of anobject (not shown) on the image sensor 100. When the image sensor 100 isaccurately located on a focal plane of the objective lens 210, a lightstarting from at a certain point of the object arrives at a certainpoint on the image sensor 100 by passing through the objective lens 210.For example, a light starting from a certain point A on an optical axisOX passes through the objective lens 210 and then arrives at a center ofthe image sensor 100 on the optical axis OX. Also, light starting fromany one of points B, C, and D located out of the optical axis OX travelsacross the optical axis OX by the objective lens 210 and arrives at apoint in a peripheral portion of the image sensor 100. For example, alight starting from the point B located above the optical axis OXarrives at a lower peripheral portion of image sensor 100, crossing theoptical axis OX, and a light starting from the point C located under theoptical axis OX arrives at an upper peripheral portion of the imagesensor 100, crossing the optical axis OX. Also, a light starting fromthe point D located between the optical axis OX and the point B arrivesat a position between the lower peripheral portion and the center ofimage sensor 100, crossing the optical axis OX.

Accordingly, the light starting from the different points A, B, C, and Dare incident on the image sensor 100 at different incident anglesaccording to the distance between the points A, B, C, and D and theoptical axis OX. An incident angle of a light incident on the imagesensor 100 is typically defined to be a chief ray angle (CRA). A chiefray (CR) denotes a light ray starting from a point of the object andarriving at the image sensor 100 by passing through a center of theobjective lens 210. The CRA denotes an angle formed by the CR withrespect to the optical axis OX. The CRA of the light starting from thepoint A on the optical axis OX is 0° and the light is perpendicularlyincident on the image sensor 100. The CRA increases as the startingpoint is farther from the optical axis OX.

From the viewpoint of the image sensor 100, the CRA of the lightincident on the center portion of the image sensor 100 is 0° and the CRAof the incident light gradually increases toward the edge of the imagesensor 100. For example, the CRA of the light starting from each of thepoints B and C and arriving at the outermost edge of the image sensor100 is the largest, whereas the CRA of the light starting from the pointA and arriving at the center of the image sensor 100 is 0°. The CRA ofthe light starting from the point D and arriving at a position betweenthe center and the edge of the image sensor 100 is greater than 0° andless than the CRA of the light starting from each of the points B and C.

However, the color separation elements 130 generally have a structurehaving directivity. Due to the directivity, the color separationelements 130 efficiently operate with respect to the lightperpendicularly incident on the color separation elements 130. However,if the incident angle increases over a certain angle, the colorseparation efficiency of the color separation elements 130 isdrastically lowered. Accordingly, when the color separation elements 130having the same structure are arranged in the entire area of the imagesensor 100, the quality of an image may be more degraded as a distancefrom the center portion of the image sensor 100 increases.

The color separation element array according to the present exemplaryembodiment may include the color separation elements 130 that areconfigured to efficiently perform color separation even at the edge ofthe image sensor 100. For example, each of the color separation elements130 may include a first element 130 a and a second element 130 b thatare sequentially arranged in the direction of the optical axis OX or atraveling direction of the incident light. The first element 130 a andthe second element 130 b of the color separation elements 130 may beshifted by different degrees according to the positions of the colorseparation elements 130 in the image sensor 100. For example, the firstelement 130 a and the second element 130 b of the color separationelement 130 at the center portion of the image sensor 100 may bearranged such that the center portions, e.g., center lines, of the firstelement 130 a and the second element 130 b may be aligned with eachother. The first element 130 a and the second element 130 b of the colorseparation element 130 arranged in an area other than the center portionof the image sensor 100 may be shifted with each other. For example, ashift distance between the first element 130 a and the second element130 b as a distance from the center portion of the image sensor 100increases. The first element 130 a and the second element 130 b of thecolor separation element 130 arranged at the outermost edge of the imagesensor 100 may be shifted to the greatest extent with respect to eachother.

FIG. 5A is a cross-sectional view exemplarily illustrating a positionalrelationship between the first element 130 a and the second element 130b of the color separation element 130 when a light is perpendicularlyincident on the image sensor 100. FIGS. 5B and 5C are cross-sectionalviews exemplarily illustrating in detail a positional relationshipbetween the first element 130 a and the second element 130 b of thecolor separation element 130 when a light is obliquely incident on theimage sensor 100.

Referring to FIG. 5A, when the incident light is perpendicularlyincident on the image sensor 100, the first element 130 a and the secondelement 130 b of the color separation element 130 are not shifted witheach other. In this case, the first element 130 a and the second element130 b of the color separation element 130 may be aligned along a centerline (not shown) of a pixel facing the color separation element 130 suchthat the center portions of the first element 130 a and the secondelement 130 b may be matched with each other. In contrast, referring toFIGS. 5B and 5C, when the incident light is obliquely incident on theimage sensor 100, the first element 130 a and the second element 130 bof the color separation element 130 may be shifted with each other. Thefirst element 130 a and the second element 130 b of the color separationelement 130 may be shifted to be aligned with the traveling direction ofa light that is obliquely incident. For example, as illustrated in FIG.5B, when the incident light is obliquely incident from the left side,the first element 130 a may be relatively further shifted to the leftcompared to the second element 130 b. Also, as illustrated in FIG. 5C,when the incident light is obliquely incident from the right side, thefirst element 130 a may be relatively further shifted to the rightcompared to the second element 130 b. A relative shift distance “d” ofthe first element 130 a and the second element 130 b gradually increasesas the incident angle of the incident light increases, that is, the CRAincreases.

As described above, when the incident light is perpendicularly incident,the color separation elements 130 may be aligned along the center lineof a pixel facing the color separation element 130. However, when theincident light is obliquely incident, the first and second elements 130a and 130 b are relatively shifted with each other according to adirection in which a light is incident. FIGS. 6A and 6B arecross-sectional views illustrating a change in the positions of thefirst element 130 a and the second element 130 b of the color separationelement 130 according to a change in a light incident angle.

For example, when the incident angle is θ1 as illustrated in FIG. 6A,the incident light may be refracted from a surface of the transparentdielectric layer 120 to travel inside the transparent dielectric layer120 at an inclined angle of α1. Then, the second element 130 b may bemoved in the direction toward the incident light such that the light C2of the second wavelength band exiting from the second element 130 baccurately travels toward the center portion of the light sensing layer111 of a pixel corresponding to the light C2 and the light C3 of thethird wavelength band travel toward the center portion of the lightsensing layer 111 of a pixel corresponding to the light C3. The firstelement 130 a is further shifted with respect to the second element 130b in the direction toward the incident light such that the first element130 a and the second element 130 b are arranged to match the inclinedangle α1. As a result, the first element 130 a may be moved by D1 fromthe center line of a pixel facing the color separation element 130.

The inclined angle α1 in which a light travels inside the transparentdielectric layer 120 may be calculated by the Snell's law. For example,an equation that n1×sin θ1=n2×sin α1 is established, where “n1” is anexternal refractive index of the image sensor 100 and “n2” is an averagerefractive index of the transparent dielectric layer 120 and the colorseparation elements 130. The average refractive index n2 is calculatedconsidering a volume ratio of the transparent dielectric layer 120 andthe color separation elements 130. Since the incident angle θ1 maycorrespond to the CRA, the angle α at which the first and secondelements 130 a and 130 b of the color separation elements 130 at aparticular position of the image sensor 100 are aligned may satisfy anequation that n1×sin(CRAi)=n2×sin α, where “CRAi” is the CRA at an i-thposition.

On the other hand, when the incident angle is θ2 that is greater than θ1as illustrated in FIG. 6B, the incident light is refracted on thesurface of the transparent dielectric layer 120 and travels inside thetransparent dielectric layer 120 at an inclined angle α2 that is greaterthan the inclined angle α1. Then, a degree that the first element 130 aand the second element 130 b are shifted in a direction toward theincident light may be increased compared to the case in FIG. 6A. As aresult, the first element 130 a may be shifted by D2 that is greaterthan D1 from the center line of a corresponding pixel such that thefirst element 130 a and the second element 130 b are arranged to matchthe inclined angle α2.

FIGS. 7A to 9B are cross-sectional views exemplarily illustrating thecolor separation elements 130 according to various exemplaryembodiments. First, referring to FIGS. 7A and 7B, the first element 130a and the second element 130 b of the color separation element 130 maybe arranged to be separated from each other by a predetermined gap g.Although FIGS. 5A to 5C illustrate that the first element 130 a and thesecond element 130 b closely contact to each other, the structurethereof is not limited thereto. As illustrated in FIGS. 7A and 7B, thefirst element 130 a and the second element 130 b may be arranged to beseparated from each other. The gap between the first element 130 a andthe second element 130 b may be less than or equal to about 50 or 100nm.

Also, referring to FIGS. 8A and 8B, the color separation element 130 mayfurther include a third element 130 c. The third element 130 c may bearranged following the second element 130 b in the traveling directionof the incident light. When the incident light is perpendicularlyincident, the first to third elements 130 a, 130 b, and 130 c of thecolor separation element 130 may be aligned along the center line of acorresponding pixel such that the center portions of the first to thirdelements 130 a, 130 b, and 130 c are matched with one another asillustrated in FIG. 8A. In contract, when the incident light isobliquely incident, the first to third elements 130 a, 130 b, and 130 cof the color separation element 130 may be shifted with respect to oneanother as illustrated in FIG. 8B. A relative shift distance d1 betweenthe first element 130 a and the second element 130 b may be the same asor different from a relative shift distance d2 between the secondelement 130 b and the third element 130 c. The shift distance d1 and theshift distance d2 may be variously selected according to an incidentangle of the incident light and a wavelength band to be separated.Although FIGS. 8A and 8B exemplarily illustrates that the colorseparation element 130 includes three elements, that is, the first tothird elements 130 a, 130 b, and 130 c, the color separation element 130may include four or more elements that are sequentially arranged in atraveling direction of the incident light.

The widths of the first to third elements 130 a, 130 b, and 130 c of thecolor separation element 130 may be the same as or different from oneanother. For example, the width of the first element 130 a located atthe foremost of the traveling direction of the incident light may be thelargest and the width of the third element 130 c located at the rearmostof the traveling direction of the incident light may be the smallest.The width of the second element 130 b may be smaller than that of thefirst element 130 a and larger than that of the third element 130 c. Asthe widths of the first to third elements 130 a, 130 b, and 130 cgradually decrease along the traveling direction of the incident light,the use of a material of the color separation elements 130 may bereduced while the color separation efficiency is maintained or improved.

On the other hand, the first to third elements 130 a, 130 b, and 130 cof the color separation element 130 may be formed of a material having ahigher refractive index than the refractive index of a surroundingportion. For example, the refractive indices of the first to thirdelements 130 a, 130 b, and 130 c may be higher than the refractive indexof the transparent dielectric layer 120. For example, the transparentdielectric layer 120 may be formed of SiO₂ or siloxane-based spin-onglass (SOG), the first to third elements 130 a, 130 b, and 130 c may beformed of a material having a high refractive index, such as, TiO₂,SiN₃, ZnS, ZnSe, and Si₃N₄. Although the first to third elements 130 a,130 b, and 130 c may have the same refractive index, differentrefractive indices may be selected to improve the color separationefficiency according to the incident angle of the incident light and awavelength band to be separated.

Although FIGS. 8A and 8B illustrate that the first to third elements 130a, 130 b, and 130 c closely contact one another, as illustrated in FIGS.9A and 9B, the first to third elements 130 a, 130 b, and 130 c may bearranged to be separated from one another. A gap g1 between the firstelement 130 a and the second element 130 b may be the same or differentfrom a gap g2 between the second element 130 b and the third element 130c. The gaps g1 and g2 may be selected based on the incident angle of theincident light and the shift distances d1 and d2 between the first tothird elements 130 a, 130 b, and 130 c, such that the first to thirdelements 130 a, 130 b, and 130 c are arranged to match the travellingdirection of the incident light. For example, both the gaps g1 and g2may be selected to be less than or equal to about 50 or 100 nm.

FIG. 10 is a plan view exemplarily illustrating shift forms of firstelements and second elements according to the positions of a pluralityof color separation elements in the image sensor 100. Referring to FIG.10, since a first element 131 a and a second element of the colorseparation element are arranged to be overlapped with each other at thecenter portion of the image sensor 100, only the first element 131 a isseen whereas the second element covered by the first element 131 a isnot seen. Also, first elements 132 a, 133 a, 134 a, 135 a, 136 a, 137 a,138 a, and 139 a and second elements 132 b, 133 b, 134 b, 135 b, 136 b,137 b, 138 b, and 139 b of the color separation elements located at aperipheral portion of the image sensor 100 are shifted with each otherin a direction x and a direction y. Since a z-axis in FIG. 10 is thesame direction as the optical axis OX, the first elements 132 a, 133 a,134 a, 135 a, 136 a, 137 a, 138 a, and 139 a and the second elements 132b, 133 b, 134 b, 135 b, 136 b, 137 b, 138 b, and 139 b may be shifted ina direction perpendicular to the optical axis OX.

For example, the first element 132 a and the second element 132 blocated in the upper area of the image sensor 100 are shifted in adirection −y; the first element 133 a and the second element 133 blocated in the lower area of the image sensor 100 are shifted in adirection +y; and the first element 134 a and the second element 134 blocated at the left area of the image sensor 100 are shifted in adirection +x. The first element 138 a and the second element 138 blocated in the lower right area of the image sensor 100 are shifted inthe direction +y and a direction −x. As illustrated in FIG. 10, thefirst elements 132 a, 133 a, 134 a, 135 a, 136 a, 137 a, 138 a, and 139a of the color separation elements arranged in a peripheral portion ofthe image sensor 100 are further shifted toward the center area comparedto the second elements 132 b, 133 b, 134 b, 135 b, 136 b, 137 b, 138 b,and 139 b. The first elements 132 a, 133 a, 134 a, 135 a, 136 a, 137 a,138 a, and 139 a and the second elements 132 b, 133 b, 134 b, 135 b, 136b, 137 b, 138 b, and 139 b may be symmetrically shifted with respect tothe center area of the image sensor 100. For example, the first elements131 a, 132 a, 133 a, 134 a, 135 a, 136 a, 137 a, 138 a, and 139 a andthe second elements 132 b, 133 b, 134 b, 135 b, 136 b, 137 b, 138 b, and139 b of the color separation elements may be shifted to be aligned witha traveling direction in the transparent dielectric layer 120 of the CRthat passed through the objective lens 210.

FIG. 11 is a graph exemplarily showing color separation efficiencyaccording to a change in a light incident angle. In the graph of FIG.11, curved lines indicated by A, B, and C denote color separationefficiencies when the first element and the second element are shiftedaccording to the incident angle of the incident light, whereas curvedlines indicated by A′, B′, and C′ denote color separation efficiencieswhen the first element and the second element are not shifted regardlessof the incident angle of the incident light. The curved lines A and A′denote color separation efficiencies of blue and red, the curved lines Band B′ denote color separation efficiencies of green, and the curvedlines C and C′ denote average color separation efficiencies of theentire colors. As it may be seen from the graph of FIG. 11, the totalaverage efficiencies C and C′ for both cases of shifting and notshifting the first element and the second element are similar to eachother. However, when the first element and the second element are notshifted, as the incident angle increases, the color separationefficiencies of blue and red decrease much and the color separationefficiency of green increases much. Accordingly, color distortion maygreatly occur in the peripheral portion of the image sensor 100. Incontrast, when the first element and the second element are shifted, achange in the color separation efficiency according to a change in theincident angle is not generated much. Accordingly, uniform colorcharacteristics may be obtained through the entire area of the imagesensor 100.

The foregoing exemplary embodiments and advantages are merely exemplaryand are not to be construed as limiting. The present teaching can bereadily applied to other types of apparatuses. Also, the description ofthe exemplary embodiments is intended to be illustrative, and not tolimit the scope of the claims, and many alternatives, modifications, andvariations will be apparent to those skilled in the art.

What is claimed is:
 1. A color separation element array comprising:color separation elements which are two-dimensionally arranged andconfigured to separate an incident light according to a wavelength suchthat, of the incident light, a light of a first wavelength is directedto a first direction and a light of a second wavelength that isdifferent from the first wavelength is directed to a second directionthat is different from the first direction, wherein each of the colorseparation elements comprises a first element and a second element thatare sequentially arranged along a traveling direction of the incidentlight, and the first element and the second element of the colorseparation elements are symmetrically shifted with respect to a centerarea of the color separation element array, to be aligned to fit to thetraveling direction of the incident light that is obliquely incident. 2.The color separation element array of claim 1, wherein the first elementand the second element of each of the color separation elements areseparated from each other such that each of the color separationelements includes a gap between the first element and the secondelement.
 3. The color separation element array of claim 1, wherein thefirst element and the second element of one of the color separationelements, which is arranged in a center area of the color separationelement array, are aligned with one another, such that center portionsof the first element and the second element are aligned, and the firstelements and the second elements of respective color separationelements, which are arranged in an area other than the center area ofthe color separation element array, are shifted with respect to oneanother, forming shifted pairs each comprising respective first andsecond elements.
 4. The color separation element array of claim 3,wherein the first elements of the shifted pairs are shifted closertoward the center area of the color separation element array than thesecond elements of corresponding shifted pairs.
 5. The color separationelement array of claim 3, wherein the shifted pairs are disposed atlocations spaced apart from the center area of the color separationelement array, and a shift amount between the first and second elementsof respective shifted pairs increases as a distance from the center areaof the color separation element array to the respective shifted pairsincreases.
 6. The color separation element array of claim 1, whereineach of the color separation elements further comprises: a third elementthat is arranged following the second element along the travelingdirection of the incident light.
 7. The color separation element arrayof claim 6, wherein a width of the second element is smaller than awidth of the first element, and a width of the third element is smallerthan the width of the second element.
 8. An image sensor comprising: apixel array comprising pixels which are two-dimensionally arranged andconfigured to detect light; and a color separation element arraycomprising color separation elements which are two-dimensionallyarranged and configured to separate an incident light according to awavelength such that the light of different wavelengths is incident ondifferent pixels, wherein each of the color separation elementscomprises a first element and a second element that are sequentiallyarranged along a traveling direction of the incident light, and thefirst element and the second element of the color separation elementsare symmetrically shifted with respect to a center area of the colorseparation element array, to be aligned to fit to the travelingdirection of the incident light that is obliquely incident.
 9. The imagesensor of claim 8, wherein the first element and the second element ofeach of the color separation elements are separated from each other suchthat each of the color separation elements includes a gap between thefirst element and the second element.
 10. The image sensor of claim 8,wherein the first element and the second element of one of the colorseparation elements, which is arranged in a center area of the colorseparation element array, are aligned with one another, such that centerportions of the first element and the second element are aligned, andthe first elements and the second elements of respective colorseparation elements, which are arranged in an area other than the centerarea of the color separation element array, are shifted from each other,forming shifted pairs each comprising respective first and secondelements.
 11. The image sensor of claim 10, wherein the first elementsof the shifted pairs are shifted closer toward the center area of thecolor separation element array than the second elements of correspondingshifted pairs.
 12. The image sensor of claim 10, wherein the shiftedpairs are disposed at locations spaced apart from the center area of thecolor separation element array, and a shift amount between the first andsecond elements of respective shifted pairs increases as a distance fromthe center area of the color separation element array to the respectiveshifted pairs increases.
 13. An image pickup apparatus comprising: anobjective lens; and an image sensor, which is configured to convert alight focused by the objective lens to an electrical image signal, andcomprises: a pixel array comprising pixels which are two-dimensionallyarranged and configured to detect the light; and a color separationelement array comprising color separation elements which aretwo-dimensionally arranged and configured to separate an incident lightaccording to a wavelength such that the light of different wavelengthsis incident on different pixels, wherein each of the color separationelements comprises a first element and a second element that aresequentially arranged along a traveling direction of the incident light,and the first element and the second element of the color separationelements are symmetrically shifted with respect to a center area of thecolor separation element array, to be aligned to fit to the travelingdirection of the incident light that is obliquely incident.
 14. Theimage pickup apparatus of claim 13, wherein the first element and thesecond element of each of the color separation elements are separatedfrom each other such that each of the color separation elements includesa gap between the first element and the second element.
 15. The imagepickup apparatus of claim 13, wherein the first element and the secondelement of one of the color separation elements, which is arranged in acenter area of the color separation element array, are aligned with oneanother, such that center portions of the first element and the secondelement are aligned, and the first elements and the second elements ofrespective color separation elements, which are arranged in an areaother than the center area of the color separation element array, areshifted with respect to one another, forming shifted pairs eachcomprising respective first and second elements.
 16. The image pickupapparatus of claim 15, wherein the shifted pairs are disposed atlocations spaced apart from the center area of the color separationelement array, the first elements of the shifted pairs are shiftedcloser toward the center area of the color separation element array thanthe second elements of corresponding shifted pairs, and a shift amountbetween the first and second elements of the corresponding shifted pairsincreases as a distance from the center area of the color separationelement array to the corresponding shifted pairs increases.
 17. Theimage pickup apparatus of claim 13, wherein the first element and thesecond element of the color separation elements are shifted to bealigned to fit to a traveling direction of a chief light that passesthrough the objective lens.
 18. The image pickup apparatus of claim 13,wherein the image sensor further comprises a transparent dielectriclayer arranged on a surface of the pixel array, and the color separationelements are buried in the transparent dielectric layer.